<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
      body{

      }
      #d1{
        color:red;
      }
      div{
        /*!important作用是提升优先级*/
        color: blue !important;
      }
    </style>
</head>
<body>
  <div id="d1">
    <p id="p1">这是个p标签</p>
    <span>这是div里面的span</span>
    <a href="">超链接</a>
  </div>
  <span>这是div外面的span</span>
</body>
</html>